Perpendicular recording at high area density requires increases of track density due to the down-track bit length approaching its smallest size achievable by state-of-the-art write head field down-track gradient. This increase of track-density demands a sharper cross-track field gradient of the writer field as well as better stability and less noise of the magnetic data track in the cross-track direction. Prior study [1] suggests that a patterned track medium, where magnetic data tracks are physically separated from each other by a non-magnetic trench or by a spacer, not only reduces reader noise pickup from erasure bands between the tracks, due to the well defined track width, but also increases on-track data stability against leakage field erasure while the writer is writing on adjacent tracks.
Fabrication of the patterned track medium has been based on two main methods [2-5]—substrate patterning and magnetic layer patterning. In the substrate patterning method, the substrate onto which the magnetic films will be deposited is first patterned into physical tracks. For magnetic layer patterning, the etching is performed after deposition of the magnetic layers and usually terminates within the intermediate layer before reaching the soft under layer (SUL). From a magnetic recording point of view, magnetic layer patterning causes less flux leakage from the SUL edges and reduces noise during read-back. However, it is more expensive to use than substrate patterning.
The actual patterning process is usually done by either ion beam or electron beam exposure of photo-resist which, after developing and baking, then serves as the mask during subsequent ion-milling or chemical etching to etch away part of the underlying substrate or magnetic layers. However, all existing methods to produce a patterned magnetic medium result in physically defined magnetic data tracks that are separated from adjacent tracks by air spacing or by spacing filled with non-magnetic materials.
Even for the gained stability and lower noise of the patterned track magnetic medium, with the track pitch going smaller, the writer pole will need to shrink accordingly if it is to avoid erasing adjacent tracks during writing of current track. This smaller size inevitably degrades the down-track gradient of the write head due to the reduced magnetic volume which, in turn, limits the highest down-track bit density achievable. It is foreseeable that the trade-off between down-track data density and cross-track data density will reach a point where further increases in track density will no longer lead to an effective increase of data area density, due to the density loss in the down-track direction.
Thus, additional head and/or media features that can enable further shrinking of track pitch, without sacrificing significant down-track field gradient, are needed. For example, the write head field in the cross-track direction is required to be confined to the limit of the boundaries of the current track. Write field confinement of this type can be achieved by fully shielding [6] or side shielding [7] the magnetic writer, where the shield structure on the sides partially cancels the field in the adjacent tracks and reduces side erasure. However, due to the spacing that already exists between the tracks in a patterned medium, write field shielding can also be implemented by a shielded structure of the kind disclosed by the present invention.    [1] X. Che, et al, “Recording Performance Study of PMR Media With Patterned Tracks,” IEEE Trans. Magn., vol. 43, pp. 2292, 2007    [2] D. E. Wachenschwanz, et al, “Perpendicular magnetic discrete track recording disk,” U.S. Pat. No. 7,147,790 B2 (2006)    [3] Y. Kamata, et al, “Method for manufacturing substrate for discrete track recording media and method for manufacturing discrete track recording media,” US Patent Pub. #: US 2007/0001331 A1 (2007)    [4] K. Nakada, K. Hattori, and S. Okawa, “Pattern drawing method, stamper manufactureing method, and pattern drawing apparatus,” US Patent Pub. #: US 2007/0023704 A1 (2007)    [5] C. Haginoya, T. Ando, and M. Ogino, “Magnetic recording medium and method for production thereof,” US Patent Pub. #: US 2007/0072013 A1 (2007)    [6] H. L. Hu, Y. S. Tang, L. Guan and K. Ju, “Fully shielded perpendicular recording writer,” US Patent Pub. #: US 2005/0083605 A1 (2005).    [7] W. P. Jayasekara, and H. S. Gill, “Laminated side shield for perpendicular write head for improved performance,” US Patent Pub. #: US 2006/0098334 A1 (2006).A routine search of the prior art was performed with the following additional references of interest being found:
U.S. Pat. No. 6,421,195 (Rubin et al) shows channels, running along radii in a direction normal to the tracks' path, separated by channel boundaries that may be magnetic and have substantially different magnetic properties than those of the channels. In U.S. Pat. No. 6,717,770, Crawford discloses tracks separated by guard bands, while U.S. Patent Application 2006/0028758 (Sakurai et al) shows tracks separated by guard bands which are a groove or non-magnetic material and in U.S. Patent Application 2006/0029834, Suwa et al. show a non-magnetic filler layer between tracks.